There are two types of optical recording media, one of which is to form physically deformed portions such as holes or concavities at a certain place of a recording layer by irradiation with beam of energy, and the other of which is to form portions having been changed in optical properties such as refractive index and reflectance at a certain place of a recording layer by irradiation with beam of energy.
Recording layers consisting essentially of low melting metal such as tellurium (Te) have heretofore been known as recording layers for the two types of the optical recording media (Japanese Pat. L-O-P Publns. Nos. 71195/1983 and 9234/1983.) Te thin film, typical of low-melting metallic films, is capable of forming thereon desired physically deformed portions or portions having been changed in optical properties (hereinafter generally called "pits") by irradiating a very low energy, and thus is very useful as a high sensitivity material. By sensitivity as used herein is meant that which is defined by energy (mJ/cm.sup.2) required for forming pits per unit surface area.
Though the recording layers consisting essentially of Te are known, optical recording media comprising conventional substrate such as a polycarbonate resin substrate and these recording layers laminated thereon have such a problem that recording sensitivity is not always sufficient. Hence, it is demanded to provide optical recording media improved in recording sensitivity.
Further, the optical recording media comprising conventional substrate such as a polycarbonate resin substrate and the recording layer consisting essentially of Te laminated thereon have still such a problem that the adhesion of the substrate to the recording layer is insufficient. Therefore, a stage for removing water contained in the polycarbonate resin to be used as the substrate is required. Further, there is sometimes required a stage for treating the surface of the polycarbonate resin substrate with plasma to improve the adhesion of the substrate to the recording layer.
With the purpose of providing an optical recording medium which is improved in recording sensitivity as well as in the adhesion between the substrate and the recording layer, the present inventors prosecuted extensive researches and have found that optical recording media excellent in recording sensitivity as well as in the adhesion between the substrate and the recording layer can be obtained when a random copolymer having a specific structure, composed of ethylene and a cycloolefin unit is used as a substrate and a specific recording layer is laminated thereon. The present inventors have eventually accomplished the present invention on the basis of this finding.
Further, a relationship between the composition of a recording layer mainly comprising Te and the oxidation thereof have been studied to improve the oxidation resistance thereof.
For example, a Te film comprising C and H, and a Cr- comprising Te film have been proposed in Japanese Pat. Publn. No. 3320/1984 and Japanese Pat. L-O-P No. 63038/1984, respectively.
However, the proposed recording layers mainly comprising Te are not sufficiently oxidation-resistant.